1. Field of the Invention
The present invention relates to a disk drive device, and in particular, to a structure for discharging static electricity charged in a disk drive device.
2. Description of the Related Art
Recently, a technique for improving a recording density of a fixed disk drive device (hereinafter, simply referred to as a disk drive device) has been rapidly developed, and with this, a recording capacity has been drastically enhanced. In such a disk drive device, data are magnetically recorded on a recording disk rotating at a high-speed. Because such a recording disk rotates at a high-speed in air, the disk is sometimes charged with static electricity. A large amount of static electricity charged in a recording disk may cause a discharge breakdown of a magnetic head or a breakdown of the data recorded on the disk. In order to prevent such a charge of static electricity in a recording disk, a conductive path for grounding the static electricity charged in the recording disk is required to be secured within a disk drive device. A disk drive device is structured with a hub supporting a recording disk, a shaft to which the hub is fixed, a bearing member housing the shaft, and a base housing (also referred to as a motor base) that houses part of the bearing member, etc., each of which can be formed of a conductive material. Accordingly, the conductive path for discharging the static electricity charged in a recording disk can be, for example, secured by electrically connecting the hub supporting a recording disk, the shaft, the bearing member and the base housing together.
When securing the conductive path among the respective components, it is better that the path is secured by direct contacts among the components; however, a reliable connection method has to be selected for the portion where components have to be firmly fixed together, such as the portion where the bearing member and the base housing are connected together. When two components are to be firmly fixed together by inserting one of the two into an opening portion of the other, such as the case of the bearing member and the base housing, press-fitting can be considered. However, in the case of the component such as the bearing member that rotatably supports the shaft, while being spaced apart by a gap of several μm from the shaft, deformation of the component has to be avoided. Therefore, it is preferable that a connection method in which an external force is hardly applied to the bearing member is adopted.
Due to the aforementioned situations, the bearing member and the base housing have been conventionally combined together by a loose fit such that the two are fixed together by filling an adhesive therebetween, in many cases. In this case, however, there is a problem that conductivity between the bearing member and the base housing cannot be secured because an adhesive is filled therebetween. Methods for securing the conductivity between the bearing member and the base housing include caulking, welding and soldering, etc.; however, these methods are not preferable, because a large external force or a high-temperature is applied to a component during work, so that the component is likely to deform. Therefore, a method using a conductive adhesive by which adhesion involving conductivity is possible, is proposed as disclosed in Japanese Patent Application Publication 2004-289982.
As stated above, the bearing member has been required to have conductivity to discharge the statistic electricity charged on the disk side via the base housing. A sleeve and a housing of which the bearing member is composed are formed of a metal such as a copper material; however, there have been demands that these components should be formed of a material that is light in weight and suitable for mass production, in terms of weight reduction or cost reduction. Even in the case, it has to be taken into account that sufficient conductivity performance is secured and the conductivity property is not varied in each product.